Looking at all the evidence, I do think your piece has some good age to it and could well be late 1800s, and certainly early 1900s, no newer than 1930.
Having looked hard and long at the mark, it's going to be impossible for me to read all four characters, it's just too degraded and indistinct. Two of the characters read 品乗 meaning "special goods" which is typical of these seals which, even when fully translated, tend to create more questions than answers. There's no formal registry of makers' seals in the West for bronze censers, and virtually none is a recognized or collected 'name' so knowing what they say is of curiosity value only, though some are helpful confirmation of the date. Collectors understand this and look for other features such as patina, rarity of form, artistic merit and so on.
As such, this would be quite a desirable piece if sold at a good antique auction house, especially one having a specialist sale of Asian bronzes.
This example, for instance, very similar to yours, sold at auction for $300 which is probably about right.
I would give yours an auction estimate in the range of $250 - $400. It therefore has a full retail value (if you saw it for sale in an antique store, say) of $750. This is also the replacement value for insurance purposes.
I do hope this helps!
Please let me know if I can be of further assistance with this, I would be glad to.